Malignant hyperthermia Flashcards
Define malignant hyperthermia
Inherited myopathy characterized by a hypermetabolic state and muscle rigidity. Susceptible patients once exposed to certain triggering agents develop a sustained increase in temperature and associated complications
What is the mortality of malignant hyperthermia
Was > 10% fallen to 2 - 10 % in recent years due to greater awareness and training
What is the inheritance of malignant hyperthermia
Autosomal dominant with variable penetrance –> 50% of children with susceptible parents are potentially at risk
Describe the genetic aetiology of MH
Mutation on the ryanodine receptor gene (RYRI) on chromosome 19q (30 -80% of families)
The ryanodine receptor gene encodes the skeletal muscle sarcoplasmic reticulum calcium release channel. The mutation impairs calcium re-uptake by the SR which leads to sustained muscle contraction and a hypermetabolic state
How does the increased intracellular calcium in malignant hyperthermia lead to a hypermetabolic state
Directly activates phosphorylase to increase glycolysis and
Indirectly because of increased demand for ATP production (needed for calcium sequestration)
What are the possible associated with MH
Strong associations
- Central core disease
Possible associates
- Patients with a tendency for heat stroke
- Strabismus
List possible MH precipitants relevant to anaesthetics
- All volatile anaesthetic agents
2. Succinylcholine
What are the early signs of malignant hyperthermia?
Sustained jaw rigidity after SUX
- may persist for several minutes at a time when relaxation would be expected
Respiratory
- Tachypnoea with increased Ve
- Increasing ETCO2
CVS
- Tachycardia
- Ventricular ectopics
- Peaked T-waves - hyperkalaemia
What are the intermediate signs and symptoms of MH
Increasing Temperature
Desaturation
Arrhythmia
ABG:
- Mixed resp/met acidosis
- Hyperkalaemia
- Hypercalcaemia
- Raised serum CK (rhabdomyolysis
What are the LATE signs and symptoms of MH
Generalized muscle rigidity Difficult ventilation (chest wall rigidity) Arrhythmias - severe Oliguria Myoglobinuria Prolonged bleeding time Death
What conditions might mimic the clinical presentation of malignant hyperthermia
A. Inadequate anaesthesia/analgesia B. Inappropriate fresh gas flow/ventilation C. Infection/sepsis D. Tourniquet ischaemia E. Anaphylaxis F. Phaeochromocytoma G. Thyroid storm
Summarize the treatment of malignant hyperthermia
- HELP
- Remove triggering agents
- Dantrolene
- Active cooling
- Supportive
- Teamwork
In the management of MH, how are triggering agents removed
Do not administer suxamethonium
Turn of all vaporizers and change to 100% O2
Use a new clean breathing circuit with high FGF
Avoid sodalime
Maintain anaesthesia with intravenous agents (propofol)
Essentially: change to a new Bains breathing circuit with high FGF, stop volatile, switch to TIVA and give dantrolene
Describe the presentation of dantrolene sodium
70 ml glass vial
Contains
- 20 mg dantrolene sodium
- 3 g mannitol and NaOH
Diluted with 60 ml H20 –> pH 9.5
How long does dantrolene take to reconstitute
up to 20 minutes to dissolve – therefore start reconstitution asap
What is the mode of action of dantrolene
Binds to the ryanodine receptor and interferes with release of calcium ions from the sarcoplasmic reticulum. Re-establishes myoplasmic calcium equilibrium
What is the dose of dantrolene
Initial: 2.5 mg/kg
Subsequent boluses of 1 mg/kg to a maximum of 10mg/kg
Describe methods used for active cooling
Cooled IV fluids Convert active warming devices to active cooling devices Ice packs in axillae Cold gastric lavage Cold peritoneal lavage Cold bladder lavage Extracorporeal heat exchange
What should patients be referred for subsequent to recovering from an episode of malignant hyperthermia
In vitro contracture testing
- muscle biopsy exposed to halothane and caffeine
99% sensitive
93% specific
Consider genetic tests also and combine these to to establish a diagnosis
Describe the general principles for administering an anaesthetic in a patient with previous episode of MH, diagnosis of MH or family hx of MH
No sux and no volatile
RA best
If GA required –> TIVA with NDNMB
Dantrolene at hand but prophylactic dantrolene not indicated
Use a vapour free anaesthetic machine (flush according to manufacturer guidelines
How to create a ‘vapour free’ anaesthetic machine if one is not already available
Remove vaporizer
High flow O2 through machine, ventilator and bellows for 20 minutes
New soda lime
New breathing circuit, bag and masks
